SR2K

So my truck has developed a strange, and oddly specific habit. When its cold out (below freezing) and the truck hasn't warmed up yet, (coolant below 130F) and its in third gear, between 1800 and 2300rpm, it makes a very loud whining or whistling sound. It sounds like its coming from under the hood but its hard to be certain. It also goes away immediately once the clutch is depressed.

Any ideas on what it could be? Is this something that is potentially damaging? A sign of something about to fail? Just a strange quirk of a 14 year old truck?

Carcrazygts2

Throw out bearing.